diff --git a/package-lock.json b/package-lock.json
index e04cc22175ee..9c19e27a7e02 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4,6 +4,16 @@
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
+    "@ampproject/remapping": {
+      "version": "0.3.0",
+      "resolved": "https://registry.npmjs.org/@ampproject/remapping/-/remapping-0.3.0.tgz",
+      "integrity": "sha512-dqmASpaTCavldZqwdEpokgG4yOXmEiEGPP3ATTsBbdXXSKf6kx8jt2fPcKhodABdZlYe82OehR2oFK1y9gwZxw==",
+      "dev": true,
+      "requires": {
+        "@jridgewell/resolve-uri": "1.0.0",
+        "sourcemap-codec": "1.4.8"
+      }
+    },
     "@babel/code-frame": {
       "version": "7.10.1",
       "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.10.1.tgz",
@@ -36,6 +46,12 @@
       "integrity": "sha512-KioOCsSvSvXx6xUNLiJz+P+VMb7NRcePjoefOr74Y5P6lEKsiOn35eZyZzgpK4XCNJdXTDR7+zykj0lwxRvZ2g==",
       "dev": true
     },
+    "@jridgewell/resolve-uri": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/@jridgewell/resolve-uri/-/resolve-uri-1.0.0.tgz",
+      "integrity": "sha512-9oLAnygRMi8Q5QkYEU4XWK04B+nuoXoxjRvRxgjuChkLZFBja0YPSgdZ7dZtwhncLBcQe/I/E+fLuk5qxcYVJA==",
+      "dev": true
+    },
     "@rollup/plugin-commonjs": {
       "version": "11.0.0",
       "resolved": "https://registry.npmjs.org/@rollup/plugin-commonjs/-/plugin-commonjs-11.0.0.tgz",
@@ -3737,9 +3753,9 @@
       }
     },
     "sourcemap-codec": {
-      "version": "1.4.6",
-      "resolved": "https://registry.npmjs.org/sourcemap-codec/-/sourcemap-codec-1.4.6.tgz",
-      "integrity": "sha512-1ZooVLYFxC448piVLBbtOxFcXwnymH9oUF8nRd3CuYDVvkRBxRl6pB4Mtas5a4drtL+E8LDgFkQNcgIw6tc8Hg==",
+      "version": "1.4.8",
+      "resolved": "https://registry.npmjs.org/sourcemap-codec/-/sourcemap-codec-1.4.8.tgz",
+      "integrity": "sha512-9NykojV5Uih4lgo5So5dtw+f0JgJX30KCNI8gwhz2J9A15wD0Ml6tjHKwf6fTSa6fAdVBdZeNOs9eJ71qCk8vA==",
       "dev": true
     },
     "spdx-correct": {
diff --git a/package.json b/package.json
index a0f0b9e455b8..19d1f715d69c 100644
--- a/package.json
+++ b/package.json
@@ -56,6 +56,7 @@
   },
   "homepage": "https://github.com/sveltejs/svelte#README",
   "devDependencies": {
+    "@ampproject/remapping": "^0.3.0",
     "@rollup/plugin-commonjs": "^11.0.0",
     "@rollup/plugin-json": "^4.0.1",
     "@rollup/plugin-node-resolve": "^6.0.0",
@@ -89,6 +90,7 @@
     "rollup": "^1.27.14",
     "source-map": "^0.7.3",
     "source-map-support": "^0.5.13",
+    "sourcemap-codec": "^1.4.8",
     "tiny-glob": "^0.2.6",
     "tslib": "^1.10.0",
     "typescript": "^3.5.3"
diff --git a/src/compiler/compile/Component.ts b/src/compiler/compile/Component.ts
index d2542c9830f0..6a70190e68e2 100644
--- a/src/compiler/compile/Component.ts
+++ b/src/compiler/compile/Component.ts
@@ -29,7 +29,9 @@ import add_to_set from './utils/add_to_set';
 import check_graph_for_cycles from './utils/check_graph_for_cycles';
 import { print, x, b } from 'code-red';
 import { is_reserved_keyword } from './utils/reserved_keywords';
+import { apply_preprocessor_sourcemap } from '../utils/string_with_sourcemap';
 import Element from './nodes/Element';
+import { DecodedSourceMap, RawSourceMap } from '@ampproject/remapping/dist/types/types';
 
 interface ComponentOptions {
 	namespace?: string;
@@ -330,6 +332,8 @@ export default class Component {
 			js.map.sourcesContent = [
 				this.source
 			];
+
+			js.map = apply_preprocessor_sourcemap(this.file, js.map, compile_options.sourcemap as (string | RawSourceMap | DecodedSourceMap));
 		}
 
 		return {
diff --git a/src/compiler/compile/index.ts b/src/compiler/compile/index.ts
index 1faa33ee1e7f..842539fcde88 100644
--- a/src/compiler/compile/index.ts
+++ b/src/compiler/compile/index.ts
@@ -11,6 +11,7 @@ const valid_options = [
 	'format',
 	'name',
 	'filename',
+	'sourcemap',
 	'generate',
 	'outputFilename',
 	'cssOutputFilename',
diff --git a/src/compiler/compile/render_dom/index.ts b/src/compiler/compile/render_dom/index.ts
index 024aafde14a0..4a767dfed120 100644
--- a/src/compiler/compile/render_dom/index.ts
+++ b/src/compiler/compile/render_dom/index.ts
@@ -7,6 +7,8 @@ import { extract_names, Scope } from '../utils/scope';
 import { invalidate } from './invalidate';
 import Block from './Block';
 import { ClassDeclaration, FunctionExpression, Node, Statement, ObjectExpression, Expression } from 'estree';
+import { apply_preprocessor_sourcemap } from '../../utils/string_with_sourcemap';
+import { RawSourceMap, DecodedSourceMap } from '@ampproject/remapping/dist/types/types';
 
 export default function dom(
 	component: Component,
@@ -30,6 +32,9 @@ export default function dom(
 	}
 
 	const css = component.stylesheet.render(options.filename, !options.customElement);
+
+	css.map = apply_preprocessor_sourcemap(options.filename, css.map, options.sourcemap as string | RawSourceMap | DecodedSourceMap);
+
 	const styles = component.stylesheet.has_styles && options.dev
 		? `${css.code}\n/*# sourceMappingURL=${css.map.toUrl()} */`
 		: css.code;
diff --git a/src/compiler/interfaces.ts b/src/compiler/interfaces.ts
index 5249c2fd48b7..689b59529d90 100644
--- a/src/compiler/interfaces.ts
+++ b/src/compiler/interfaces.ts
@@ -110,6 +110,7 @@ export interface CompileOptions {
 	filename?: string;
 	generate?: 'dom' | 'ssr' | false;
 
+	sourcemap?: object | string;
 	outputFilename?: string;
 	cssOutputFilename?: string;
 	sveltePath?: string;
diff --git a/src/compiler/preprocess/index.ts b/src/compiler/preprocess/index.ts
index 1d7d74ceac03..1de41cf9bf2f 100644
--- a/src/compiler/preprocess/index.ts
+++ b/src/compiler/preprocess/index.ts
@@ -1,6 +1,11 @@
+import { RawSourceMap, DecodedSourceMap } from '@ampproject/remapping/dist/types/types';
+import { decode as decode_mappings } from 'sourcemap-codec';
+import { getLocator } from 'locate-character';
+import { StringWithSourcemap, sourcemap_add_offset, combine_sourcemaps } from '../utils/string_with_sourcemap';
+
 export interface Processed {
 	code: string;
-	map?: object | string;
+	map?: string | object;  // we are opaque with the type here to avoid dependency on the remapping module for our public types.
 	dependencies?: string[];
 }
 
@@ -37,12 +42,18 @@ function parse_attributes(str: string) {
 interface Replacement {
 	offset: number;
 	length: number;
-	replacement: string;
+	replacement: StringWithSourcemap;
 }
 
-async function replace_async(str: string, re: RegExp, func: (...any) => Promise<string>) {
+async function replace_async(
+	filename: string,
+	source: string,
+	get_location: ReturnType<typeof getLocator>,
+	re: RegExp,
+	func: (...any) => Promise<StringWithSourcemap>
+): Promise<StringWithSourcemap> {
 	const replacements: Array<Promise<Replacement>> = [];
-	str.replace(re, (...args) => {
+	source.replace(re, (...args) => {
 		replacements.push(
 			func(...args).then(
 				res =>
@@ -55,16 +66,55 @@ async function replace_async(str: string, re: RegExp, func: (...any) => Promise<
 		);
 		return '';
 	});
-	let out = '';
+	const out = new StringWithSourcemap();
 	let last_end = 0;
 	for (const { offset, length, replacement } of await Promise.all(
 		replacements
 	)) {
-		out += str.slice(last_end, offset) + replacement;
+		// content = unchanged source characters before the replaced segment
+		const content = StringWithSourcemap.from_source(
+			filename, source.slice(last_end, offset), get_location(last_end));
+		out.concat(content).concat(replacement);
 		last_end = offset + length;
 	}
-	out += str.slice(last_end);
-	return out;
+	// final_content = unchanged source characters after last replaced segment
+	const final_content = StringWithSourcemap.from_source(
+		filename, source.slice(last_end), get_location(last_end));
+	return out.concat(final_content);
+}
+
+/** 
+ * Convert a preprocessor output and its leading prefix and trailing suffix into StringWithSourceMap  
+ */
+function get_replacement(
+	filename: string,
+	offset: number,
+	get_location: ReturnType<typeof getLocator>,
+	original: string,
+	processed: Processed,
+	prefix: string,
+	suffix: string
+): StringWithSourcemap {
+
+	// Convert the unchanged prefix and suffix to StringWithSourcemap
+	const prefix_with_map = StringWithSourcemap.from_source(
+		filename, prefix, get_location(offset));
+	const suffix_with_map = StringWithSourcemap.from_source(
+		filename, suffix, get_location(offset + prefix.length + original.length));
+
+	// Convert the preprocessed code and its sourcemap to a StringWithSourcemap
+	let decoded_map: DecodedSourceMap;
+	if (processed.map) {
+		decoded_map = typeof processed.map === 'string' ? JSON.parse(processed.map) : processed.map;
+		if (typeof(decoded_map.mappings) === 'string') {
+			decoded_map.mappings = decode_mappings(decoded_map.mappings);
+		}
+		sourcemap_add_offset(decoded_map, get_location(offset + prefix.length));
+	}
+	const processed_with_map = StringWithSourcemap.from_processed(processed.code, decoded_map);
+
+	// Surround the processed code with the prefix and suffix, retaining valid sourcemappings
+	return prefix_with_map.concat(processed_with_map).concat(suffix_with_map);
 }
 
 export default async function preprocess(
@@ -76,60 +126,92 @@ export default async function preprocess(
 	const filename = (options && options.filename) || preprocessor.filename; // legacy
 	const dependencies = [];
 
-	const preprocessors = Array.isArray(preprocessor) ? preprocessor : [preprocessor];
+	const preprocessors = preprocessor
+		? Array.isArray(preprocessor) ? preprocessor : [preprocessor]
+		: [];
 
 	const markup = preprocessors.map(p => p.markup).filter(Boolean);
 	const script = preprocessors.map(p => p.script).filter(Boolean);
 	const style = preprocessors.map(p => p.style).filter(Boolean);
 
+	// sourcemap_list is sorted in reverse order from last map (index 0) to first map (index -1)
+	// so we use sourcemap_list.unshift() to add new maps
+	// https://github.com/ampproject/remapping#multiple-transformations-of-a-file
+	const sourcemap_list: Array<DecodedSourceMap | RawSourceMap> = [];
+
+	// TODO keep track: what preprocessor generated what sourcemap? to make debugging easier = detect low-resolution sourcemaps in fn combine_mappings
+
 	for (const fn of markup) {
+
+		// run markup preprocessor
 		const processed = await fn({
 			content: source,
 			filename
 		});
-		if (processed && processed.dependencies) dependencies.push(...processed.dependencies);
-		source = processed ? processed.code : source;
+
+		if (!processed) continue;
+
+		if (processed.dependencies) dependencies.push(...processed.dependencies);
+		source = processed.code;
+		if (processed.map) {
+			sourcemap_list.unshift(
+				typeof(processed.map) === 'string'
+					? JSON.parse(processed.map)
+					: processed.map
+			);
+		}
 	}
 
-	for (const fn of script) {
-		source = await replace_async(
+	async function preprocess_tag_content(tag_name: 'style' | 'script', preprocessor: Preprocessor) {
+		const get_location = getLocator(source);
+		const tag_regex = tag_name == 'style' 
+			? /<!--[^]*?-->|<style(\s[^]*?)?(?:>([^]*?)<\/style>|\/>)/gi
+			: /<!--[^]*?-->|<script(\s[^]*?)?(?:>([^]*?)<\/script>|\/>)/gi;
+
+		const res = await replace_async(
+			filename,
 			source,
-			/<!--[^]*?-->|<script(\s[^]*?)?(?:>([^]*?)<\/script>|\/>)/gi,
-			async (match, attributes = '', content = '') => {
+			get_location,
+			tag_regex,
+			async (match, attributes = '', content = '', offset) => {
+				const no_change = () => StringWithSourcemap.from_source(
+					filename, match, get_location(offset));
 				if (!attributes && !content) {
-					return match;
+					return no_change();
 				}
 				attributes = attributes || '';
-				const processed = await fn({
+				content = content || '';
+
+				// run script preprocessor
+				const processed = await preprocessor({
 					content,
 					attributes: parse_attributes(attributes),
 					filename
 				});
-				if (processed && processed.dependencies) dependencies.push(...processed.dependencies);
-				return processed ? `<script${attributes}>${processed.code}</script>` : match;
+
+				if (!processed) return no_change();
+				if (processed.dependencies) dependencies.push(...processed.dependencies);
+				return get_replacement(filename, offset, get_location, content, processed, `<${tag_name}${attributes}>`, `</${tag_name}>`);
 			}
 		);
+		source = res.string;
+		sourcemap_list.unshift(res.map);
+	}
+
+	for (const fn of script) {
+		await preprocess_tag_content('script', fn);
 	}
 
 	for (const fn of style) {
-		source = await replace_async(
-			source,
-			/<!--[^]*?-->|<style(\s[^]*?)?(?:>([^]*?)<\/style>|\/>)/gi,
-			async (match, attributes = '', content = '') => {
-				if (!attributes && !content) {
-					return match;
-				}
-				const processed: Processed = await fn({
-					content,
-					attributes: parse_attributes(attributes),
-					filename
-				});
-				if (processed && processed.dependencies) dependencies.push(...processed.dependencies);
-				return processed ? `<style${attributes}>${processed.code}</style>` : match;
-			}
-		);
+		await preprocess_tag_content('style', fn);
 	}
 
+	// Combine all the source maps for each preprocessor function into one
+	const map: RawSourceMap = combine_sourcemaps(
+		filename,
+		sourcemap_list
+	);
+
 	return {
 		// TODO return separated output, in future version where svelte.compile supports it:
 		// style: { code: styleCode, map: styleMap },
@@ -138,7 +220,7 @@ export default async function preprocess(
 
 		code: source,
 		dependencies: [...new Set(dependencies)],
-
+		map: (map as object),
 		toString() {
 			return source;
 		}
diff --git a/src/compiler/utils/string_with_sourcemap.ts b/src/compiler/utils/string_with_sourcemap.ts
new file mode 100644
index 000000000000..7f8a0ec1eba0
--- /dev/null
+++ b/src/compiler/utils/string_with_sourcemap.ts
@@ -0,0 +1,275 @@
+import { DecodedSourceMap, RawSourceMap, SourceMapLoader } from '@ampproject/remapping/dist/types/types';
+import remapping from '@ampproject/remapping';
+import { SourceMap } from 'magic-string';
+
+type SourceLocation = {
+	line: number;
+	column: number;
+};
+
+function last_line_length(s: string) {
+	return s.length - s.lastIndexOf('\n') - 1;
+}
+
+// mutate map in-place
+export function sourcemap_add_offset(
+	map: DecodedSourceMap, offset: SourceLocation
+) {
+	if (map.mappings.length == 0) return map;
+	// shift columns in first line
+	const segment_list = map.mappings[0];
+	for (let segment = 0; segment < segment_list.length; segment++) {
+		const seg = segment_list[segment];
+		if (seg[3]) seg[3] += offset.column;
+	}
+	// shift lines
+	for (let line = 0; line < map.mappings.length; line++) {
+		const segment_list = map.mappings[line];
+		for (let segment = 0; segment < segment_list.length; segment++) {
+			const seg = segment_list[segment];
+			if (seg[2]) seg[2] += offset.line;
+		}
+	}
+}
+
+function merge_tables<T>(this_table: T[], other_table: T[]): [T[], number[], boolean, boolean] {
+	const new_table = this_table.slice();
+	const idx_map = [];
+	other_table = other_table || [];
+	let val_changed = false;
+	for (const [other_idx, other_val] of other_table.entries()) {
+		const this_idx = this_table.indexOf(other_val);
+		if (this_idx >= 0) {
+			idx_map[other_idx] = this_idx;
+		} else {
+			const new_idx = new_table.length;
+			new_table[new_idx] = other_val;
+			idx_map[other_idx] = new_idx;
+			val_changed = true;
+		}
+	}
+	let idx_changed = val_changed;
+	if (val_changed) {
+		if (idx_map.find((val, idx) => val != idx) === undefined) {
+			// idx_map is identity map [0, 1, 2, 3, 4, ....]
+			idx_changed = false;
+		}
+	}
+	return [new_table, idx_map, val_changed, idx_changed];
+}
+
+function pushArray<T>(_this: T[], other: T[]) {
+	// We use push to mutate in place for memory and perf reasons
+	// We use the for loop instead of _this.push(...other) to avoid the JS engine's function argument limit (65,535 in JavascriptCore)
+	for (let i = 0; i < other.length; i++) {
+		_this.push(other[i]);
+	}
+}
+
+export class StringWithSourcemap {
+	string: string;
+	map: DecodedSourceMap;
+
+	constructor(string = '', map: DecodedSourceMap = null) {
+		this.string = string;
+		if (map) {
+			this.map = map as DecodedSourceMap;
+		} else {
+			this.map = {
+				version: 3,
+				mappings: [],
+				sources: [],
+				names: []
+			};
+		}
+	}
+
+	/**
+	 * concat in-place (mutable), return this (chainable)
+	 * will also mutate the `other` object
+	 */
+	concat(other: StringWithSourcemap): StringWithSourcemap {
+		// noop: if one is empty, return the other
+		if (other.string == '') return this;
+		if (this.string == '') {
+			this.string = other.string;
+			this.map = other.map;
+			return this;
+		}
+
+		this.string += other.string;
+
+		const m1 = this.map;
+		const m2 = other.map;
+
+		if (m2.mappings.length == 0) return this;
+
+		// combine sources and names
+		const [sources, new_source_idx, sources_changed, sources_idx_changed] = merge_tables(m1.sources, m2.sources);
+		const [names, new_name_idx, names_changed, names_idx_changed] = merge_tables(m1.names, m2.names);
+
+		if (sources_changed) m1.sources = sources;
+		if (names_changed) m1.names = names;
+
+		// unswitched loops are faster
+		if (sources_idx_changed && names_idx_changed) {
+			for (let line = 0; line < m2.mappings.length; line++) {
+				const segment_list = m2.mappings[line];
+				for (let segment = 0; segment < segment_list.length; segment++) {
+					const seg = segment_list[segment];
+					if (seg[1]) seg[1] = new_source_idx[seg[1]];
+					if (seg[4]) seg[4] = new_name_idx[seg[4]];
+				}
+			}
+		} else if (sources_idx_changed) {
+			for (let line = 0; line < m2.mappings.length; line++) {
+				const segment_list = m2.mappings[line];
+				for (let segment = 0; segment < segment_list.length; segment++) {
+					const seg = segment_list[segment];
+					if (seg[1]) seg[1] = new_source_idx[seg[1]];
+				}
+			}
+		} else if (names_idx_changed) {
+			for (let line = 0; line < m2.mappings.length; line++) {
+				const segment_list = m2.mappings[line];
+				for (let segment = 0; segment < segment_list.length; segment++) {
+					const seg = segment_list[segment];
+					if (seg[4]) seg[4] = new_name_idx[seg[4]];
+				}
+			}
+		}
+
+		// combine the mappings
+
+		// combine
+		// 1. last line of first map
+		// 2. first line of second map
+		// columns of 2 must be shifted
+
+		const column_offset = last_line_length(this.string);
+		if (m2.mappings.length > 0 && column_offset > 0) {
+			const first_line = m2.mappings[0];
+			for (let i = 0; i < first_line.length; i++) {
+				first_line[i][0] += column_offset;
+			}
+		}
+
+		// combine last line + first line
+		pushArray(m1.mappings[m1.mappings.length - 1], m2.mappings.shift());
+
+		// append other lines
+		pushArray(m1.mappings, m2.mappings);
+
+		return this;
+	}
+
+	static from_processed(string: string, map?: DecodedSourceMap): StringWithSourcemap {
+		if (map) return new StringWithSourcemap(string, map);
+		if (string == '') return new StringWithSourcemap();
+		map = { version: 3, names: [], sources: [], mappings: [] };
+
+		// add empty SourceMapSegment[] for every line
+		const line_count = (string.match(/\n/g) || '').length;
+		for (let i = 0; i < line_count; i++) map.mappings.push([]);
+		return new StringWithSourcemap(string, map);
+	}
+
+	static from_source(
+		source_file: string, source: string, offset?: SourceLocation
+	): StringWithSourcemap {
+		if (!offset) offset = { line: 0, column: 0 };
+		const map: DecodedSourceMap = { version: 3, names: [], sources: [source_file], mappings: [] };
+		if (source == '') return new StringWithSourcemap(source, map);
+
+		// we create a high resolution identity map here,
+		// we know that it will eventually be merged with svelte's map,
+		// at which stage the resolution will decrease.
+		const line_list = source.split('\n');
+		for (let line = 0; line < line_list.length; line++) {
+			map.mappings.push([]);
+			const token_list = line_list[line].split(/([^\d\w\s]|\s+)/g);
+			for (let token = 0, column = 0; token < token_list.length; token++) {
+				if (token_list[token] == '') continue;
+				map.mappings[line].push([column, 0, offset.line + line, column]);
+				column += token_list[token].length;
+			}
+		}
+		// shift columns in first line
+		const segment_list = map.mappings[0];
+		for (let segment = 0; segment < segment_list.length; segment++) {
+			segment_list[segment][3] += offset.column;
+		}
+		return new StringWithSourcemap(source, map);
+	}
+}
+
+export function combine_sourcemaps(
+	filename: string,
+	sourcemap_list: Array<DecodedSourceMap | RawSourceMap>
+): RawSourceMap {
+	if (sourcemap_list.length == 0) return null;
+
+	let map_idx = 1;
+	const map: RawSourceMap =
+		sourcemap_list.slice(0, -1)
+			.find(m => m.sources.length !== 1) === undefined
+
+			? remapping( // use array interface
+				// only the oldest sourcemap can have multiple sources
+				sourcemap_list,
+				() => null,
+				true // skip optional field `sourcesContent`
+			)
+
+			: remapping( // use loader interface
+				sourcemap_list[0], // last map
+				function loader(sourcefile) {
+					if (sourcefile === filename && sourcemap_list[map_idx]) {
+						return sourcemap_list[map_idx++]; // idx 1, 2, ...
+						// bundle file = branch node
+					}
+					else return null; // source file = leaf node
+				} as SourceMapLoader,
+				true
+			);
+
+	if (!map.file) delete map.file; // skip optional field `file`
+
+	return map;
+}
+
+// browser vs node.js
+const b64enc = typeof btoa == 'function' ? btoa : b => Buffer.from(b).toString('base64');
+
+export function apply_preprocessor_sourcemap(filename: string, svelte_map: SourceMap, preprocessor_map_input: string | DecodedSourceMap | RawSourceMap): SourceMap {
+	if (!svelte_map || !preprocessor_map_input) return svelte_map;
+
+	const preprocessor_map = typeof preprocessor_map_input === 'string' ? JSON.parse(preprocessor_map_input) : preprocessor_map_input;
+
+	const result_map = combine_sourcemaps(
+		filename,
+		[
+			svelte_map as RawSourceMap,
+			preprocessor_map
+		]
+	) as RawSourceMap;
+
+	// Svelte expects a SourceMap which includes toUrl and toString. Instead of wrapping our output in a class,
+	// we just tack on the extra properties.
+	Object.defineProperties(result_map, {
+		toString: {
+			enumerable: false,
+			value: function toString() {
+				return JSON.stringify(this);
+			}
+		},
+		toUrl: {
+			enumerable: false,
+			value: function toUrl() {
+				return 'data:application/json;charset=utf-8;base64,' + b64enc(this.toString());
+			}
+		}
+	});
+
+	return result_map as SourceMap;
+}
diff --git a/test/preprocess/index.ts b/test/preprocess/index.ts
index 60d3acbabb6c..be898bbbfdc0 100644
--- a/test/preprocess/index.ts
+++ b/test/preprocess/index.ts
@@ -24,6 +24,9 @@ describe('preprocess', () => {
 				config.options || { filename: 'input.svelte' }
 			);
 			fs.writeFileSync(`${__dirname}/samples/${dir}/_actual.html`, result.code);
+			if (result.map) {
+				fs.writeFileSync(`${__dirname}/samples/${dir}/_actual.html.map`, JSON.stringify(result.map, null, 2));
+			}
 
 			assert.equal(result.code, expected);
 
diff --git a/test/setup.js b/test/setup.js
index 7406a07dd9fb..74250c10ebe0 100644
--- a/test/setup.js
+++ b/test/setup.js
@@ -12,7 +12,7 @@ require.extensions['.js'] = function(module, filename) {
 		.replace(/^import (\w+) from ['"]([^'"]+)['"];?/gm, 'var {default: $1} = require("$2");')
 		.replace(/^import {([^}]+)} from ['"](.+)['"];?/gm, 'var {$1} = require("$2");')
 		.replace(/^export default /gm, 'exports.default = ')
-		.replace(/^export (const|let|var|class|function) (\w+)/gm, (match, type, name) => {
+		.replace(/^export (const|let|var|class|function|async\s+function) (\w+)/gm, (match, type, name) => {
 			exports.push(name);
 			return `${type} ${name}`;
 		})
diff --git a/test/sourcemaps/helpers.ts b/test/sourcemaps/helpers.ts
new file mode 100644
index 000000000000..d0bea310e623
--- /dev/null
+++ b/test/sourcemaps/helpers.ts
@@ -0,0 +1,20 @@
+import MagicString from 'magic-string';
+
+export function magic_string_preprocessor_result(filename: string, src: MagicString) {
+	return {
+		code: src.toString(),
+		map: src.generateMap({
+			source: filename,
+			hires: true,
+			includeContent: false
+		})
+	};
+}
+
+export function magic_string_replace_all(src: MagicString, search: string, replace: string) {
+	let idx = src.original.indexOf(search);
+	if (idx == -1) throw new Error('search not found in src');
+	do {
+		src.overwrite(idx, idx + search.length, replace, { storeName: true });
+	} while ((idx = src.original.indexOf(search, idx + 1)) != -1);
+}
diff --git a/test/sourcemaps/index.ts b/test/sourcemaps/index.ts
index 7659948744be..4122c3a41969 100644
--- a/test/sourcemaps/index.ts
+++ b/test/sourcemaps/index.ts
@@ -37,7 +37,7 @@ describe('sourcemaps', () => {
 			const preprocessed = await svelte.preprocess(
 				input.code,
 				config.preprocess || {},
-				{
+				config.options || {
 					filename: 'input.svelte'
 				}
 			);
@@ -46,8 +46,10 @@ describe('sourcemaps', () => {
 				preprocessed.code, {
 				filename: 'input.svelte',
 				// filenames for sourcemaps
+				sourcemap: preprocessed.map,
 				outputFilename: `${outputName}.js`,
-				cssOutputFilename: `${outputName}.css`
+				cssOutputFilename: `${outputName}.css`,
+				...(config.compile_options || {})
 			});
 
 			js.code = js.code.replace(
@@ -107,7 +109,7 @@ describe('sourcemaps', () => {
 			css.mapConsumer = css.map && await new SourceMapConsumer(css.map);
 			css.locate = getLocator(css.code || '');
 			css.locate_1 = getLocator(css.code || '', { offsetLine: 1 });
-			test({ assert, input, preprocessed, js, css });
+			await test({ assert, input, preprocessed, js, css });
 		});
 	});
 });
diff --git a/test/sourcemaps/samples/compile-option-dev/_config.js b/test/sourcemaps/samples/compile-option-dev/_config.js
new file mode 100644
index 000000000000..b6ea851b6dd6
--- /dev/null
+++ b/test/sourcemaps/samples/compile-option-dev/_config.js
@@ -0,0 +1,21 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	compile_options: {
+		dev: true
+	},
+	preprocess: [
+		{ style: ({ content, filename }) =>  {
+				const src = new MagicString(content);
+				magic_string_replace_all(src, '--replace-me-once', '\n --done-replace-once');
+				magic_string_replace_all(src, '--replace-me-twice', '\n--almost-done-replace-twice');
+				return magic_string_preprocessor_result(filename, src);
+		} },
+		{ style: ({ content, filename }) =>  {
+				const src = new MagicString(content);
+				magic_string_replace_all(src, '--almost-done-replace-twice', '\n  --done-replace-twice');
+				return magic_string_preprocessor_result(filename, src);
+		} }
+	]
+};
diff --git a/test/sourcemaps/samples/compile-option-dev/input.svelte b/test/sourcemaps/samples/compile-option-dev/input.svelte
new file mode 100644
index 000000000000..6d5f91158dbe
--- /dev/null
+++ b/test/sourcemaps/samples/compile-option-dev/input.svelte
@@ -0,0 +1,15 @@
+<h1>Testing Styles</h1>
+<h2>Testing Styles 2</h2>
+<div>Testing Styles 3</div>
+<script>export const b = 2;</script>
+<style>
+	h1 {
+		--replace-me-once: red;
+	}
+	h2 {
+		--replace-me-twice: green;
+	}
+	div {
+		--keep-me: blue;
+	}
+</style>
diff --git a/test/sourcemaps/samples/compile-option-dev/test.js b/test/sourcemaps/samples/compile-option-dev/test.js
new file mode 100644
index 000000000000..bf240a5a8927
--- /dev/null
+++ b/test/sourcemaps/samples/compile-option-dev/test.js
@@ -0,0 +1,40 @@
+import { SourceMapConsumer } from 'source-map';
+
+const b64dec = s => Buffer.from(s, 'base64').toString();
+
+export async function test({ assert, css,  js }) {
+
+    // We check that the css source map embedded in the js is accurate
+    const match = js.code.match(/\tstyle\.textContent = "(.*?)(?:\\n\/\*# sourceMappingURL=data:(.*?);charset=(.*?);base64,(.*?) \*\/)?";\n/);
+	assert.notEqual(match, null);
+
+	const [mimeType, encoding, cssMapBase64] = match.slice(2);
+	assert.equal(mimeType, 'application/json');
+	assert.equal(encoding, 'utf-8');
+
+	const cssMapJson = b64dec(cssMapBase64);
+	css.mapConsumer = await new SourceMapConsumer(cssMapJson);
+
+	// TODO make util fn + move to test index.js
+	const sourcefile = 'input.svelte';
+	[
+		// TODO how to get line + column numbers?
+		[css, '--keep-me', 13, 2],
+		[css, '--done-replace-once', 6, 5],
+		[css, '--done-replace-twice', 9, 5]
+	]
+	.forEach(([where, content, line, column]) => {
+		assert.deepEqual(
+			where.mapConsumer.originalPositionFor(
+				where.locate_1(content)
+			),
+			{
+				source: sourcefile,
+				name: null,
+				line,
+				column
+			},
+			`failed to locate "${content}" from "${sourcefile}"`
+		);
+	});
+}
diff --git a/test/sourcemaps/samples/decoded-sourcemap/_config.js b/test/sourcemaps/samples/decoded-sourcemap/_config.js
new file mode 100644
index 000000000000..dd4eee9461e0
--- /dev/null
+++ b/test/sourcemaps/samples/decoded-sourcemap/_config.js
@@ -0,0 +1,15 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+
+	js_map_sources: [], // test component has no scripts
+
+	preprocess: {
+		markup: ({ content, filename }) => {
+			const src = new MagicString(content);
+			magic_string_replace_all(src, 'replace me', 'success');
+			return magic_string_preprocessor_result(filename, src);
+		}
+	}
+};
diff --git a/test/sourcemaps/samples/decoded-sourcemap/input.svelte b/test/sourcemaps/samples/decoded-sourcemap/input.svelte
new file mode 100644
index 000000000000..b233d7f670d7
--- /dev/null
+++ b/test/sourcemaps/samples/decoded-sourcemap/input.svelte
@@ -0,0 +1,2 @@
+<h1>decoded-sourcemap</h1>
+<div>replace me</div>
diff --git a/test/sourcemaps/samples/decoded-sourcemap/test.js b/test/sourcemaps/samples/decoded-sourcemap/test.js
new file mode 100644
index 000000000000..5a44ee83cf7b
--- /dev/null
+++ b/test/sourcemaps/samples/decoded-sourcemap/test.js
@@ -0,0 +1,19 @@
+export function test({ assert, input, preprocessed }) {
+
+  const expected = input.locate('replace me');
+
+  const start = preprocessed.locate('success');
+
+  const actualbar = preprocessed.mapConsumer.originalPositionFor({
+    line: start.line + 1,
+    column: start.column
+  });
+
+  assert.deepEqual(actualbar, {
+    source: 'input.svelte',
+    name: 'replace me',
+    line: expected.line + 1,
+    column: expected.column
+  });
+
+}
diff --git a/test/sourcemaps/samples/preprocessed-markup/_config.js b/test/sourcemaps/samples/preprocessed-markup/_config.js
new file mode 100644
index 000000000000..0b2baeb49c05
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-markup/_config.js
@@ -0,0 +1,12 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	preprocess: {
+		markup: ({ content, filename }) =>  {
+			const src = new MagicString(content);
+			magic_string_replace_all(src, 'baritone', 'bar');
+			return magic_string_preprocessor_result(filename, src);
+		}
+	}
+};
diff --git a/test/sourcemaps/samples/preprocessed-markup/input.svelte b/test/sourcemaps/samples/preprocessed-markup/input.svelte
new file mode 100644
index 000000000000..ee4b90372acd
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-markup/input.svelte
@@ -0,0 +1,5 @@
+<script>
+	export let foo;
+</script>
+
+{foo.baritone.baz}
diff --git a/test/sourcemaps/samples/preprocessed-markup/test.js b/test/sourcemaps/samples/preprocessed-markup/test.js
new file mode 100644
index 000000000000..b58710396917
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-markup/test.js
@@ -0,0 +1,32 @@
+export function test({ assert, input, js }) {
+	const expectedBar = input.locate('baritone.baz');
+	const expectedBaz = input.locate('.baz');
+
+	let start = js.locate('bar.baz');
+
+	const actualbar = js.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbar, {
+		source: 'input.svelte',
+		name: 'baritone',
+		line: expectedBar.line + 1,
+		column: expectedBar.column
+	});
+
+	start = js.locate('.baz');
+
+	const actualbaz = js.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbaz, {
+		source: 'input.svelte',
+		name: null,
+		line: expectedBaz.line + 1,
+		column: expectedBaz.column
+	});
+}
diff --git a/test/sourcemaps/samples/preprocessed-multiple/_config.js b/test/sourcemaps/samples/preprocessed-multiple/_config.js
new file mode 100644
index 000000000000..39259a02a8e3
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-multiple/_config.js
@@ -0,0 +1,25 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	preprocess: {
+		markup: ({ content, filename }) => {
+			const src = new MagicString(content);
+			magic_string_replace_all(src, 'baritone', 'bar');
+			magic_string_replace_all(src, '--bazitone', '--baz');
+			return magic_string_preprocessor_result(filename, src);
+		},
+		script: ({ content, filename }) => {
+			const src = new MagicString(content);
+			const idx = content.indexOf('bar');
+			src.prependLeft(idx, '      ');
+			return magic_string_preprocessor_result(filename, src);
+		},
+		style: ({ content, filename }) => {
+			const src = new MagicString(content);
+			const idx = content.indexOf('--baz');
+			src.prependLeft(idx, '      ');
+			return magic_string_preprocessor_result(filename, src);
+		}
+	}
+};
diff --git a/test/sourcemaps/samples/preprocessed-multiple/input.svelte b/test/sourcemaps/samples/preprocessed-multiple/input.svelte
new file mode 100644
index 000000000000..e656d399ae04
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-multiple/input.svelte
@@ -0,0 +1,9 @@
+<script>
+	export let foo = { baritone: 5 }
+</script>
+<style>
+	h1 {
+		background-color: var(--bazitone);
+	}
+</style>
+<h1>multiple {foo}</h1>
diff --git a/test/sourcemaps/samples/preprocessed-multiple/test.js b/test/sourcemaps/samples/preprocessed-multiple/test.js
new file mode 100644
index 000000000000..a0cfe1fa8a4f
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-multiple/test.js
@@ -0,0 +1,32 @@
+export function test({ assert, input, js, css }) {
+	const expectedBar = input.locate('baritone');
+	const expectedBaz = input.locate('--bazitone');
+
+	let start = js.locate('bar');
+
+	const actualbar = js.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbar, {
+		source: 'input.svelte',
+		name: 'baritone',
+		line: expectedBar.line + 1,
+		column: expectedBar.column
+	});
+
+	start = css.locate('--baz');
+
+	const actualbaz = css.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbaz, {
+		source: 'input.svelte',
+		name: '--bazitone',
+		line: expectedBaz.line + 1,
+		column: expectedBaz.column
+	});
+}
diff --git a/test/sourcemaps/samples/preprocessed-script/_config.js b/test/sourcemaps/samples/preprocessed-script/_config.js
new file mode 100644
index 000000000000..94bd83c22ff6
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-script/_config.js
@@ -0,0 +1,12 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	preprocess: {
+		script: ({ content, filename }) =>  {
+			const src = new MagicString(content);
+			magic_string_replace_all(src, 'baritone', 'bar');
+			return magic_string_preprocessor_result(filename, src);
+		}
+	}
+};
diff --git a/test/sourcemaps/samples/preprocessed-script/input.svelte b/test/sourcemaps/samples/preprocessed-script/input.svelte
new file mode 100644
index 000000000000..11586619e1a0
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-script/input.svelte
@@ -0,0 +1,9 @@
+<style>
+	h1 {
+		color: red;
+	}
+</style>
+<script>
+	export let foo = { baritone: { baz: 5 } }
+</script>
+<h1>{foo.bar.baz}</h1>
diff --git a/test/sourcemaps/samples/preprocessed-script/test.js b/test/sourcemaps/samples/preprocessed-script/test.js
new file mode 100644
index 000000000000..20a366f6d290
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-script/test.js
@@ -0,0 +1,32 @@
+export function test({ assert, input, js }) {
+	const expectedBar = input.locate('baritone:');
+	const expectedBaz = input.locate('baz:');
+
+	let start = js.locate('bar:');
+
+	const actualbar = js.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbar, {
+		source: 'input.svelte',
+		name: 'baritone',
+		line: expectedBar.line + 1,
+		column: expectedBar.column
+	}, "couldn't find bar: in source");
+
+	start = js.locate('baz:');
+
+	const actualbaz = js.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbaz, {
+		source: 'input.svelte',
+		name: null,
+		line: expectedBaz.line + 1,
+		column: expectedBaz.column
+	}, "couldn't find baz: in source");
+}
diff --git a/test/sourcemaps/samples/preprocessed-styles/_config.js b/test/sourcemaps/samples/preprocessed-styles/_config.js
new file mode 100644
index 000000000000..04c8bcda7a54
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-styles/_config.js
@@ -0,0 +1,12 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	preprocess: {
+		style: ({ content, filename }) =>  {
+			const src = new MagicString(content);
+			magic_string_replace_all(src, 'baritone', 'bar');
+			return magic_string_preprocessor_result(filename, src);
+		}
+	}
+};
diff --git a/test/sourcemaps/samples/preprocessed-styles/input.svelte b/test/sourcemaps/samples/preprocessed-styles/input.svelte
new file mode 100644
index 000000000000..0d942390f4b8
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-styles/input.svelte
@@ -0,0 +1,12 @@
+<h1>Testing Styles</h1>
+<h2>Testing Styles 2</h2>
+<script>export const b = 2;</script>
+<style>
+	h1 {
+		--baritone: red;
+	}
+
+	h2 {
+		--baz: blue;
+	}
+</style>
diff --git a/test/sourcemaps/samples/preprocessed-styles/test.js b/test/sourcemaps/samples/preprocessed-styles/test.js
new file mode 100644
index 000000000000..5b28a1251481
--- /dev/null
+++ b/test/sourcemaps/samples/preprocessed-styles/test.js
@@ -0,0 +1,32 @@
+export function test({ assert, input, css }) {
+	const expectedBar = input.locate('--baritone');
+	const expectedBaz = input.locate('--baz');
+
+	let start = css.locate('--bar');
+
+	const actualbar = css.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbar, {
+		source: 'input.svelte',
+		name: null,
+		line: expectedBar.line + 1,
+		column: expectedBar.column
+	}, "couldn't find bar in source");
+
+	start = css.locate('--baz');
+
+	const actualbaz = css.mapConsumer.originalPositionFor({
+		line: start.line + 1,
+		column: start.column
+	});
+
+	assert.deepEqual(actualbaz, {
+		source: 'input.svelte',
+		name: null,
+		line: expectedBaz.line + 1,
+		column: expectedBaz.column
+	}, "couldn't find baz in source");
+}
diff --git a/test/sourcemaps/samples/sourcemap-names/_config.js b/test/sourcemaps/samples/sourcemap-names/_config.js
new file mode 100644
index 000000000000..c8557ba46528
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-names/_config.js
@@ -0,0 +1,33 @@
+import MagicString from 'magic-string';
+import { magic_string_preprocessor_result, magic_string_replace_all } from '../../helpers';
+
+export default {
+	preprocess: [
+		{
+			markup: ({ content, filename }) => {
+				const src = new MagicString(content);
+				magic_string_replace_all(src, 'baritone', 'bar');
+				magic_string_replace_all(src,'--bazitone', '--baz');
+				magic_string_replace_all(src,'old_name_1', 'temp_new_name_1');
+				magic_string_replace_all(src,'old_name_2', 'temp_new_name_2');
+				return magic_string_preprocessor_result(filename, src);
+			}
+		},
+		{
+			markup: ({ content, filename }) => {
+				const src = new MagicString(content);
+				magic_string_replace_all(src, 'temp_new_name_1', 'temp_temp_new_name_1');
+				magic_string_replace_all(src, 'temp_new_name_2', 'temp_temp_new_name_2');
+				return magic_string_preprocessor_result(filename, src);
+			}
+		},
+		{
+			markup: ({ content, filename }) => {
+				const src = new MagicString(content);
+				magic_string_replace_all(src, 'temp_temp_new_name_1', 'new_name_1');
+				magic_string_replace_all(src, 'temp_temp_new_name_2', 'new_name_2');
+				return magic_string_preprocessor_result(filename, src);
+			}
+		}
+	]
+};
diff --git a/test/sourcemaps/samples/sourcemap-names/input.svelte b/test/sourcemaps/samples/sourcemap-names/input.svelte
new file mode 100644
index 000000000000..b62715a85713
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-names/input.svelte
@@ -0,0 +1,12 @@
+<script>
+	export let old_name_1 = { baritone: 5 };
+	let old_name_2 = 'value_2';
+</script>
+<style>
+	div {
+		background-color: var(--bazitone);
+	}
+</style>
+<h1>use-names</h1>
+<div>{old_name_1.baritone}</div>
+<pre style="color: var(--bazitone)">{old_name_2}</pre>
diff --git a/test/sourcemaps/samples/sourcemap-names/test.js b/test/sourcemaps/samples/sourcemap-names/test.js
new file mode 100644
index 000000000000..cd70bd25ce90
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-names/test.js
@@ -0,0 +1,42 @@
+// needed for workaround, TODO remove
+import { getLocator } from 'locate-character';
+
+export function test({ assert, preprocessed, js, css }) {
+
+	assert.deepEqual(
+		preprocessed.map.names.sort(),
+		['baritone', '--bazitone', 'old_name_1', 'old_name_2'].sort()
+	);
+
+	function test_name(old_name, new_name, where) {
+
+		let loc = { character: -1 };
+		while (loc = where.locate(new_name, loc.character + 1)) {
+			const actualMapping = where.mapConsumer.originalPositionFor({
+				line: loc.line + 1, column: loc.column
+			});
+			if (actualMapping.line === null) {
+				// location is not mapped - ignore
+				continue;
+			}
+			assert.equal(actualMapping.name, old_name);
+		}
+		if (loc === undefined) {
+			// workaround for bug in locate-character, TODO remove
+			// https://github.com/Rich-Harris/locate-character/pull/5
+			where.locate = getLocator(where.code);
+		}
+	}
+
+	test_name('baritone', 'bar', js);
+	test_name('baritone', 'bar', preprocessed);
+
+	test_name('--bazitone', '--baz', css);
+	test_name('--bazitone', '--baz', preprocessed);
+
+	test_name('old_name_1', 'new_name_1', js);
+	test_name('old_name_1', 'new_name_1', preprocessed);
+
+	test_name('old_name_2', 'new_name_2', js);
+	test_name('old_name_2', 'new_name_2', preprocessed);
+}
diff --git a/test/sourcemaps/samples/sourcemap-sources/_config.js b/test/sourcemaps/samples/sourcemap-sources/_config.js
new file mode 100644
index 000000000000..97024cea5f59
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-sources/_config.js
@@ -0,0 +1,60 @@
+/* eslint-disable import/no-duplicates */
+/* the code that transforms these to commonjs, can't handle "MagicString, { Bundle } from.." */
+
+import MagicString from 'magic-string';
+import { Bundle } from 'magic-string';
+
+
+function add(bundle, filename, source) {
+	bundle.addSource({
+		filename,
+		content: new MagicString(source),
+		separator: '\n'
+		//separator: '' // ERROR. probably a bug in magic-string
+	});
+}
+
+function result(bundle, filename) {
+	return {
+		code: bundle.toString(),
+		map: bundle.generateMap({
+			file: filename,
+			includeContent: false,
+			hires: true // required for remapping
+		})
+	};
+}
+
+export default {
+	js_map_sources: [
+		'input.svelte',
+		'foo.js',
+		'bar.js',
+		'foo2.js',
+		'bar2.js'
+	],
+	preprocess: [
+		{
+			script: ({ content, filename }) => {
+				const bundle = new Bundle();
+
+				add(bundle, filename, content);
+				add(bundle, 'foo.js', 'var answer = 42; // foo.js\n');
+				add(bundle, 'bar.js', 'console.log(answer); // bar.js\n');
+
+				return result(bundle, filename);
+			}
+		},
+		{
+			script: ({ content, filename }) => {
+				const bundle = new Bundle();
+
+				add(bundle, filename, content);
+				add(bundle, 'foo2.js', 'var answer2 = 84; // foo2.js\n');
+				add(bundle, 'bar2.js', 'console.log(answer2); // bar2.js\n');
+
+				return result(bundle, filename);
+			}
+		}
+	]
+};
diff --git a/test/sourcemaps/samples/sourcemap-sources/input.svelte b/test/sourcemaps/samples/sourcemap-sources/input.svelte
new file mode 100644
index 000000000000..33c8a9d9a66b
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-sources/input.svelte
@@ -0,0 +1,4 @@
+<script>
+	export let name;
+</script>
+<h1>sourcemap-sources</h1>
diff --git a/test/sourcemaps/samples/sourcemap-sources/test.js b/test/sourcemaps/samples/sourcemap-sources/test.js
new file mode 100644
index 000000000000..78a4c80a1748
--- /dev/null
+++ b/test/sourcemaps/samples/sourcemap-sources/test.js
@@ -0,0 +1,29 @@
+export function test({ assert, preprocessed, js }) {
+
+	assert.equal(preprocessed.error, undefined);
+
+	// sourcemap stores location only for 'answer = 42;'
+	// not for 'var answer = 42;'
+	[
+		[js, 'foo.js', 'answer = 42;', 4],
+		[js, 'bar.js', 'console.log(answer);', 0],
+		[js, 'foo2.js', 'answer2 = 84;', 4],
+		[js, 'bar2.js', 'console.log(answer2);', 0]
+	]
+	.forEach(([where, sourcefile, content, column]) => {
+
+		assert.deepEqual(
+			where.mapConsumer.originalPositionFor(
+				where.locate_1(content)
+			),
+			{
+				source: sourcefile,
+				name: null,
+				line: 1,
+				column
+			},
+			`failed to locate "${content}" from "${sourcefile}"`
+		);
+
+	});
+}